Perform modifications of the decapeptide, lutenizing hormone releasing hormone, which should yield: long-lived antagonists of LH-RH; irreversible inhibitors; and new information on structure-function relationships of the LH-RH molecule in order to provide useful contraceptives. Peptides will be synthesized by the solid phase method where possible. Purified, chemically characterized LH-RH analogs will be supplied to the Project Officer for biological testing by the Contraceptive Development Branch, NICHD.